@Graham Wilson
Actually, the reason the state of grammar teaching is so woefully inadequate in the UK is that hardliners like yourself give a very bad impression of what good grammar really is.
Contractions are sloppiness -- they're part of the language and have always been. They are entirely necessary and inevitable in a stress-timed language, and English is a stress-timed language. A sentence such as "I wouldn't've been in the house" gets two natural stresses, and if you try to enunciate every word fully as "I would not have been in the house", you just won't be able to fit it to the natural rhythm and you will end up stressing something that you didn't intend to.
I never hear your sort complaining about French, which has codified the contracted forms as the one and only correct form -- "J'ai" but never "Je ai"; "je n'en ai (pas)" and never "je ne en ai pas" etc. In fact, this may be one of the contributing factors to the failure of English grammar teaching -- the "contracted form" is in reality the base form, and the so-called "full form" is really the *emphatic* form. By trying to claim that the emphatic form is the unmarked form, you fail to connect with the student's internal model, and cause them to reject everything that you're trying to teach them.
With regards to "tsunami", there's several things I could say. The consonant cluster /ts/ only occurs in syllable codas in English -- it is not available in syllable onsets. Consider the word "garage", which is also a borrowing. Do you say "GARage" or "garAGE"? If you compare the two, the -GE ending sounds different in them. How so? Because the the French-like GE of garAGE is only possible in the coda of stressed syllables in English. When the stress shifted to the first syllable (to better match the underlying patterns of English) it naturally resulted in a change of consonant quality. Either way, I bet you don't pronounce it with a French R. Similar, I bet you don't enunciate the first O in the borrowings "potato" and "tomato". And finally, can you tell me the stressed mora in the Japanese word "tsunami" (or even if it has one at all) and do you pronounce it with the correct pitch accent when you say it? I doubt it.
The whole 's/s' thing is another pointless mess, arising from a failure to look at the nature of the genitive in modern English. The "plural possessive" doesn't actually match the internal model of the native speaker, where the possessive suffix/clitic 's is appended to a genitive, and as we all know (or would if we studied grammar properly), the English genitive (aka the "classifier noun") is always singular. For example "bread knife" and "toothbrush". Your "greenhouse" is full of greenS, plural. This is the reason that we only pronounce one S in plural possessive -- because there is only one S: the possessive S, not the plural. The orthographic distinction between s' and 's has no analogue in the native grammar.
It's you sort that convinces people that grammar is valueless, so why not leave the matter to people who actually understand the matter?
(And for the record, I'm a native speaker and I got first class honours in English Language at uni.)